Most Americans likely know at least a little about the signs of a stroke.
While early intervention is vital for a positive outcome, medical experts also stress the need to prevent strokes, which the Stroke Foundation reports are the fifth leading cause of death in the U.S. The key to prevention is knowing what causes these brain attacks.
According to the American Heart Association, a stroke occurs when a blood vessel to the brain either bursts — a hemorrhagic stroke — or is blocked by a blood clot, which is called an ischemic stroke. The rupture or clot prevents parts of the brain from receiving oxygen, and those oxygen-starved brain cells die.
But what causes the conditions that lead to stroke?
Ischemic stroke
The main cause of ischemic strokes, which account for 87 percent of all strokes, is atherosclerosis. These fatty deposits, known as plaque, line blood vessel walls and cause blockages.
Atherosclerosis can cause two types of blockages:
A cerebral thrombosis, or blood clot, develops at the site of a blockage in the brain, preventing oxygenated blood from moving through the vessels normally.
A cerebral embolism occurs when a blood clot forms in the heart or another large artery elsewhere in the body. A piece of the clot breaks loose and travels through the blood vessels in the brain. When the clot reaches a vessel too small to pass through, it gets trapped and blocks the blood flow in that vessel.
A main cause of embolism is an irregular heartbeat known as atrial fibrillation, or AFib. Atrial fibrillation is the most common type of irregular heartbeat, affecting about five million people in the U.S.
Hemorrhagic stroke
Hemorrhagic strokes, which make up about 13 percent of stroke cases, occur when a weak blood vessel ruptures, causing bleeding into the surrounding brain tissue. As the blood accumulates, it causes compression that blocks blood flow to parts of the brain.
According to the AHA, two types of bleeding occur with hemorrhagic strokes. Intracerebral hemorrhage is bleeding within the brain, while subarachnoid hemorrhage occurs between the layers of tissue surrounding the brain.
There are two main causes of hemorrhagic strokes:
A cerebral aneurysm is a weak spot in a blood vessel that gets bigger over time, causing a “ballooning” effect. If the aneurysm ruptures, it causes bleeding into the tissue surrounding the rupture.
Though aneurysms can occur at any age, they are most common in people ages 30 to 60. They typically develop at branching points in arteries.
There are several risk factors for aneurysms, including high blood pressure, smoking, drug use, infections and brain trauma.
An arteriovenous malformation is a tangle of blood vessels that alter how oxygen flows in the bloodstream. Normally, arteries carry oxygenated blood through the brain, and veins carry the blood, now oxygen-depleted, back to the heart and lungs.
When a malformation occurs, the tangle of vessels bypasses the brain tissue and carries blood directly from the arteries to the veins, according to the AHA.
TIAs
Along with ischemic and hemorrhagic strokes are transient ischemic attacks, or TIAs. According to the AHA, TIAs are temporary blockages caused by clots that dissolve on their own, usually within five minutes of onset.
TIAs do not cause permanent damage, but medical experts call them “warning strokes,” meaning that they could be a harbinger of a larger, full-blown stroke in the near future.
Like other types of strokes, risk factors for a TIA include AFib, high blood pressure, diabetes, heart disease and smoking.
Cryptogenic stroke
A cryptogenic stroke is a stroke in which a cause cannot be determined. According to the AHA, about 1 in 3 ischemic strokes are cryptogenic.
Some potential hidden causes of these strokes include AFib, a blood clotting disorder, an undetected hardening of the arteries or problems with the heart’s structure.
Whatever the cause of a stroke, the Stroke Foundation estimates that about 80 percent of strokes are preventable. The key to prevention is controlling certain medical conditions, such as high blood pressure, high cholesterol, diabetes and certain heart diseases.
Eating a healthy diet low in saturated fat and high in fiber goes a long way toward preventing or controlling these conditions. Regular physical activity is also crucial for keeping the heart strong and keeping blood pressure and cholesterol levels in check. Smokers, who have twice the risk of stroke as nonsmokers, should talk to their doctors about ways to quit. Alcohol, which can increase blood pressure, should be used in moderation.
